1. Field of the Invention
This invention relates to an electrically-actuated throttle device for a general-purpose engine.
2. Description of the Related Art
In recent years, electrically-actuated throttle devices have come to be applied to general-purpose internal combustion engines used as prime movers in generators, agricultural machines and various other equipment for regulating the speed (rpm) of the engine by utilizing an electrically-driven actuator to open and close a throttle valve installed in the air intake passage. Japanese Laid-Open Patent Application No. Hei 4(1992)-116256, for example, teaches an electrically-actuated throttle device that uses an electrically-driven actuator to open and close not only a throttle valve but also a choke valve.
Most electrically-actuated throttle devices use a stepper motor as the electrically-driven actuator. In such a case, the electrically-driven actuator has to be initialized before the control is commenced. Namely, processing needs to be conducted for setting the rotor (output shaft) of each stepper motor to the initial position, i.e., for setting the opening of the associated valve to the initial opening, usually fully closed or fully opened. Conventionally, this has been done when the operator powers up the machine, by simultaneously supplying current to the electrically-driven actuator and then carrying out the initialization processing.
However, supplying current to the electrically-driven actuator simultaneously with power-up degrades engine starting performance because heavy consumption of battery power occurs before the engine starts and this decreases the amount of power that can be supplied to the starter motor for starting the engine. And if the engine should not be started after power-on, the battery is liable to go dead or become excessively discharged faster than otherwise.